1. Field of the Invention
The subject invention relates to fittings for high pressure and vacuum fluid lines used in environments where high purity is necessary.
2. Description of the Prior Art
Many industrial processes require controlled amounts of very pure gases. Even small amounts of ambient gas or other contaminants can adversely affect the manufacturing process. The pure flows of gas typically are delivered to a specified location in a manufacturing plant by systems of pipes. Valves may be incorporated into the system to precisely control the flow of gas. Fittings may be employed selectively in the system to properly direct a flow of gas to selected locations in the manufacturing facility.
Pipe systems for carrying very pure flows of gases generally do not rely upon welded connections because the weldment may include contaminants that can leak into the system. Additionally, the weld location often defines a weak point that can be affected adversely by vibration or shock.
Additionally, most pipe systems for carrying very pure flows of gases cannot rely upon plastic or elastomeric components that are in communication with the gas flow stream. Plastic and elastomeric components are known to cause a leaching of contaminants into the gas stream. In view of the above, connections of one pipe to another or connections of a pipe to a fitting or valve typically are carried out with threaded metallic couplings.
The typical prior art fitting for a high pressure fluid line includes first and second tubular metallic components having fluid passages extending therethrough. Each component has a mating face to be disposed in juxtaposed relationship to the mating face of the other component. The mating faces each may be characterized by a toroidal sealing bead disposed to register with the toroidal sealing bead of the other component. The components are urged axially toward one another by threaded members. For example, a first of the two components may have an array of external threads integrally formed thereon. The second of the two components may have a shoulder facing in a direction away from the mating face. A nut may be mounted over a second component and may include an inwardly extending flange dimensioned for engaging the shoulder on the second component. The nut may include an array of threads for threadable engagement with the threads formed on the first component. Threaded engagement of the nut with the threads on the first component will urge the mating faces of the two components toward one another. An annular metallic gasket typically is disposed between the mating faces. Thus, the mating faces, and in particular the toroidal sealing beads on the respective mating faces, will be urged into tight sealing engagement with the gasket.
Other prior art fittings include first and second substantially identical components. The first and second components each include a mating face and a shoulder facing away from the mating face. First and second components of such a prior art fitting are used with a mateable pair of male and female nuts. Each nut will include an inwardly extending flange dimensioned for engaging the shoulder on the component. Tightening of the nuts together will cause the inwardly extending flanges on the nuts to engage the shoulders on the coupling components. Thus, threaded tightening of the nuts will urge the coupling components toward one another and into sealing engagement with a gasket disposed therebetween.
Rotation of one or both nuts in the prior art fitting will cause the flange of the nut to wipe over the shoulder of the associated fitting component. Friction between the flange and the shoulder can transmit rotational forces from the nut to the component. Thus, one component may rotate relative to the opposed component. This rotation typically is small, but will cause a wiping of one mating face against the gasket. This wiping can cause a galling or scratching of the mating face, and particularly of the toroidal sealing bead on the mating face. Galling or scratching can be generated each time the coupling is connected and disconnected. The surface discontinuities associated with such galling or scratching can define paths for gas leakage into or out of the fluid coupling. As noted above many industrial processes require very pure gas flows. Galling or scratching can enable the leakage of ambient air into the gas stream and can adversely affect the purity of the gas flowing through a fitting. As a result, it is desirable to prevent rotation of coupling components during the connection of the components with one another.
Some prior art coupling components have included complex and costly arrangements of ball bearings disposed between the flange on the coupling nut and the shoulder on the component being coupled. The costs associated with such ball bearing fixtures make those fixtures undesirable.
A very effective prior art fitting for substantially preventing rotation is shown in U.S. Pat. No. 5,350,205 which is assigned to the assignee of the subject invention. The fitting shown in U.S. Pat. No. 5,350,205 includes a thrust bearing disposed between the flange on the coupling nut and the shoulder on the component being coupled. The thrust bearing is formed from a material having a hardness greater than the hardness of the coupling component with which it is used. The coupling nut used adjacent the thrust bearing is formed from a material that is harder than the thrust bearing. For example, the thrust bearing shown in U.S. Pat. No. 5,350,205 may be formed from a cobalt chromium-nickel alloy provided with a thin coating of silver.
The fitting shown in U.S. Pat. No. 5,350,205 has performed well. However, there is a desire to provide even further improvements.
Components of such gas flow systems are manufactured and partly assembled in ultra clean environments maintained by the manufacturer of such gas flow systems. These components or subassemblies of such components then are transported to the industrial facility that will use the system to deliver highly pure flows of specified gases. The manufacturer of pipes, fittings and valves for such gas flow systems typically will take steps to prevent contamination during transportation. These steps will include sealing the system from ambient atmosphere and charging the system with an acceptable high pressure gas, such as nitrogen. The seals are intended to prevent either an inflow or an outflow of gas. Pressurized nitrogen is intended to prevent a migration of the lower pressure ambient air into the sealed system.
The sealing of the system typically is carried out by merely threadedly engaging a cap over the mating end of a pipe that will subsequently be connected to other parts of a gas flow system. A gasket initially may be positioned in the cap. Thus, threaded tightening of the cap onto the pipe, nipple or other such component will urge the gasket into sealing engagement with the toroidal sealing bead on the mating end of the pipe. Upon delivery of the piping system subassembly to the installation site, the cap will be threadedly removed and the mating end will be joined to other components in the system in the conventional manner described above.
Sealing caps as described above are used in other instances as well. For example, an industrial facility utilizing highly pure gas flows frequently will be reconfigured to meet changing product demands. Reconfigurations of this type may involve sealing off a section of the gas flow system. The prior art threaded cap with a gasket positioned therein may be utilized for this sealing-off of portions of the system. The threaded cap may eventually be removed if and when the system is reconfigured.
Portions of a system may be sealed periodically to permit a purging of at least a section of the system. The above-described prior art sealing caps are threadedly tightened onto the mating end of a pipe in the system and the system is subjected to a pressurized flow of a purging gas. Upon completion of the purging, the sealing cap may be removed and the mating end of the previously sealed pipe may be reconnected to other parts of the system.
Leakage of contaminants into a highly pure gas flow system can occur if the mating faces of components in the system are galled, scratched or otherwise damaged. More particularly, gaskets may not adequately seal surface discontinuities caused by galling or scratching, and hence the surface discontinuity may define a passage for contaminants to travel into the gas flow system. Damage to the mating face of a fitting can occur if another metal component is wiped across the mating face. This can occur, for example, when the above described sealing cap is rotatably tightened against the toroidal sealing bead of the prior art fitting. Thus, the prior art sealing cap that is intended to prevent contamination actually can lead to contamination during a subsequent reconnection of the fitting.
The subject invention is directed to a fitting comprising at least one tubular component and at least one nut, the tubular component and the nut have engagement faces that preferably are aligned in a plane extending perpendicular to the axis of the tubular component and perpendicular to the rotational axis of the nut. Thus, rotational engagement of the nut with an array of mateable threads will urge the engagement face of the nut toward the engagement face of the tubular component,
To prevent torsion forces of the nut from being transferred to the tubular component, the fitting further comprises a smooth planar metallic member positioned adjacent the engagement face of the tubular component and a smooth planar slip member disposed between the metallic member and the engagement face of the nut. The slip member comprises a material having a very low coefficient of friction when positioned adjacent other metallic members of the fitting. For example, the slip member may be a disc or annular washer consisting of PTFE, or may comprise a disc or annular washer comprising a very hard material, such as stainless steel, coated with PTFE.
In one embodiment, the subject invention is directed to a fitting comprising first and second generally tubular components having mating faces. The mating faces may include toroidal sealing beads disposed and dimensioned for substantial registration with one another. A gasket may be disposed between the mating faces. One or both of the coupling components is provided with a shoulder facing away from the mating face. A coupling nut is mounted over the coupling component having the shoulder. The coupling nut includes an inwardly extending flange dimensioned to lie substantially in registration with the shoulder of the coupling component.
The fitting of the subject invention further includes a slip washer and a retaining ring. The slip washer preferably is formed from a very hard material, such as stainless steel coated with PTFE (Teflon). The slip washer is disposed to lie adjacent the inwardly extending flange on the nut. The retaining ring preferably is a split annular ring formed from stainless steel. The split configuration enables the retaining ring to be radially collapsed for insertion into the nut. The retaining ring then may be expanded to lock the slip washer in place adjacent the shoulder on the nut. The slip washer enables the nut to transmit axial forces to the coupling component without transmitting rotational forces. Thus, the mating faces of the coupling components can be urged axially toward or away from one another without rotational wiping therebetween. As a result, galling of the respective mating faces will not occur and a high quality seal can be achieved even after repeated connections and disconnections.
In another embodiment, the subject invention is directed to a non-rotational gas-tight cap assembly. The assembly includes a cap having a substantially tubular side wall with first and second ends. The cap is substantially opened at the second end of the tubular side wall. However, an end wall extends continuously across the cap at the first end of the tubular side wall. The tubular side wall of the cap further includes an internal circumferentially generated surface extending from the open second end of the tubular side wall to the end wall of the cap. The internal surface of the cap includes an array of internal threads for threaded engagement with a fitting to be sealed. The internal surface region of the tubular side wall may include a non-threaded portion extending between the threads and the end wall of the cap.
The non-rotational gas-tight cap assembly further includes a seal assembly. The seal assembly comprises a sealing gasket, a slip disk and a carrier for maintaining the sealing gasket and the slip disk in substantially adjacent face-to-face relationship with one another. The sealing gasket is formed from a metal material that will exhibit appropriate sealing characteristics when urged against the mating face of the fitting to be sealed. Preferably, the sealing gasket is a substantially planar metallic member having a circular periphery larger than the outside diameter of the portion of the mating face to be sealed, but smaller than the inside diameter of the cap. For example, the outside diameter of the sealing gasket may be slightly larger than the outside diameter of the toroidal sealing bead on the fitting. The preferred sealing gasket is formed from nickel.
The slip disk of the seal assembly preferably is formed from a substantially inert material that is easily rotatable relative to the sealing gasket. For example, the slip disk may be formed from PTFE (Teflon) or from metal coated with PTFE. The slip disk also may be a substantially planar member with a circular periphery and a diameter substantially equal to the diameter of the sealing gasket.
The carrier functions to hold the sealing gasket and the slip disk in face-to-face relationship with one another. The carrier may be formed from stainless steel and may include a substantially planar end wall having a substantially circular periphery defining a diameter equal to or slightly greater than the diameters of the sealing gasket and slip disk, but smaller than the inside diameter of the opening in the cap. The carrier further includes a plurality of retaining fingers projecting from the end wall. The retaining fingers are dimensioned to engage the sealing gasket and the slip disk therebetween. Portions of the retaining fingers remote from the end wall of the carrier may be angled inwardly for trapping the sealing gasket and the slip disk.
The cap assembly of the subject invention is employed by initially mounting the seal assembly into the cap such that the circular end wall of the carrier is adjacent to the end wall of the cap. The cap then is engaged rotatably with the threads on the fitting to be sealed. Tightening of the cap onto the fitting to be sealed will urge the sealing gasket into sealing engagement with the mating face of the fitting. Tightening of the cap, however, will not generate rotational movement of the sealing gasket relative to the mating face of the fitting. Rather, the slip disk disposed between the sealing gasket and the end wall of the carrier will isolate the sealing gasket from the torque generated by the cap. Thus, the cap assembly can be tightly sealed with the fitting without damaging the mating face of the fitting.
In an alternate embodiment, the carrier may be an axially short substantially cylindrical ring formed from a plastic material and having a stepped inner circumferential surface. The inner circumferential surface at one end of the plastic carrier ring may be configured and dimensioned for receiving and frictionally retaining the sealing gasket and slip disk therein. The inner circumferential surface at the opposed end of the carrier may be dimensioned for frictional mounting on the end of the fitting. In this embodiment, the plastic carrier, the sealing gasket and the slip disk may be preassembled and then may be mounted onto the end of the fitting to be sealed. This subassembly is visually observable to provide a clear indication that the subassembly is present and properly positioned before tightening the cap onto the fitting.